1. Field of the Invention
The present invention generally relates to the field of semiconductor power devices. More particularly, the present invention relates to a trench type power transistor device having super-junction structures and a method thereof.
2. Description of the Prior Art
Power devices are used in power management; for example, in switchable power supplies, management integrated circuits in the core or in the peripheral region of computers, backlight power supplies, and in electric motor controls. The type of power devices described above include an insulated gate bipolar transistor (IGBT), a metal-oxide-semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT) and so forth.
Please refer to FIG. 1, which is a schematic, cross-sectional diagram showing a structure of a conventional trench type power transistor device. As shown in FIG. 1, the conventional trench type power transistor device 10 includes an N-type substrate 12, an N-type epitaxial layer 14, a plurality of trenches 16, a gate isolation layer 18, a plurality of gates 20 and a source metal layer 22. The N-type epitaxial layer 14 is disposed on the N-type substrate 12 and each trench 16 is located on the N-type epitaxial layer 14. The gate isolating layer 18 covers the surface of each trench 16 and each gate 20 is filled into each trench 16. The function of the gate isolating layer 18 is to electrically isolate each gate 20 from the source metal layer 22. A plurality of P-type doped base regions 24 is formed on the N-type epitaxial layer 14. An N-type doped source region 26 is formed on each P-type doped base region 24 where a P-type doped contact region 28 can be implanted. Each P-type doped contact region 28 is electrically connected to the source metal layer 22 through a metal contact 30. Furthermore, a drain metal layer 32 is disposed on the bottom of the N-type substrate 12 in the conventional trench type power transistor device 10.
In order to enhance the voltage sustaining ability of trench type power transistor devices, in some cases, N-type and P-type epitaxial layers are alternately disposed so that several parallel PN junctions are formed on the N-type substrate. Power transistor devices having above-mentioned parallel PN junctions are also called super-junction power transistor devices. However, since an overlapped area between a gate structure and an N-type epitaxial layer (also called drain region) in this power transistor device is relatively high, and the thickness of a gate dielectric layer between the gate structure and the N-type epitaxial layer is relatively thin, these will cause relatively high Miller capacitance and produce inevitable switching losses. As a result, the performance of the devices is lowered.
In light of the above, there is still a need to invent an improved power transistor device which is capable of overcoming the shortcomings and deficiencies of the prior art.